This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C xc2xa7119 from an application entitled Display Apparatus With Power Interruption Delay Function earlier filed in the Korean Industrial Property Office on 30 Aug. 1996, and there duly assigned Serial No. 96-37143 by that Office.
1. Field of the Invention
The present invention relates in general to a display device employing a cathode ray tube, and more particularly to a display device with a power interruption delay function, in which a power interruption delay charging circuit is provided to prevent a horizontal output transistor from being damaged due to an instantaneous surge current generated when power supply is resumed under the condition that a high voltage charged on a horizontal deflection coil and an S-correction capacitor is not sufficiently discharged after power interruption.
2. Description of the Prior Art
Generally, a horizontal deflection circuit is supplied with power from a power supply circuit and controlled in operation by a microcomputer. Such a horizontal deflection circuit is an essential component of a display device.
Generally, in a display device a power supply circuit is adapted to convert commercial alternating current (AC) input power into direct current (DC) power to supply desired voltages to the horizontal deflection circuit and a control unit incorporating a microcomputer. The microcomputer is adapted to control the operations of the horizontal deflection circuit and the power supply circuit. The horizontal deflection circuit is adapted to horizontally deflect electron beams emitted from a cathode ray tube. An exemplary horizontal deflection circuit may include a pulse width modulation (PWM) controller for generating a PWM signal under the control of the microcomputer, a current amplifier for amplifying current in response to the PWM signal from the PWM controller, a horizontal/vertical (H/V) processor for driving a horizontal driver under the control of the microcomputer, an H/V processor constant voltage circuit for supplying a constant voltage to the H/V processor to drive it, and a horizontal output circuit for supplying current to a horizontal deflection coil and an S-correction capacitor in response to output signals from the current amplifier and horizontal driver.
The operation of the horizontal deflection circuit of the exemplary display device with the above-mentioned construction will hereinafter be described.
When the display device is powered on, the PWM controller is operated under the control of the microcomputer to output the PWM signal to the current amplifier and a high voltage from the high voltage source is transferred to the horizontal deflection coil and the S-correction capacitor.
Under the above condition, the H/V processor outputs a horizontal pulse signal of square wave to the horizontal driver under the control of the microcomputer. As a result, the high voltage charged on the horizontal deflection coil and S-correction capacitor is discharged to a ground voltage terminal.
Thereafter, when the square wave pulse signal from the H/V processor is changed from high to low in level, and the high voltage from the horizontal deflection coil and S-correction capacitor is no longer discharged.
Then, the high voltage from the high voltage source is again transferred to the horizontal deflection coil and S-correction capacitor. Hence, the above-mentioned operation is repeated.
Noticeably, the horizontal deflection coil is mounted to a neck portion of a display device so that electron beams can be deflected to the left or right according to a direction of current flowing through the coil.
The S-correction capacitor applies a parabola voltage to the horizontal deflection coil to correct a linearity of center-to-left and right sides of a screen of the display device. The S-correction capacitor also performs a DC interruption function for preventing DC current from flowing to the horizontal deflection coil.
If the power supply to the display device is interrupted during the operation of the display device, the H/V processor constant voltage circuit operates no longer due to interruption of the voltage. As a result, the H/V processor operates no longer, as well.
As the H/V processor operates no longer, it outputs no pulse signal thereby causing the high voltage charged on the horizontal deflection coil and S-correction capacitor not to be discharged. As a result, a voltage of about +120 to 160 V remains.
Under the above condition, if the power supply to the display device is resumed, the H/V processor constant voltage circuit is driven because of application of a voltage so as to operate the H/V processor, a high voltage with a very high peak value (about +1.5 to 1.8 KV) is instantaneously generated. As a result, a surge current resulting from the instantaneous high voltage abruptly flows through a discharge loop damaging a portion of the horizontal output circuit.
If the horizontal output circuit is damaged, no horizontal deflection is performed on the screen of the display device, thereby causing a single line to be vertically drawn on the center of the screen. As a result, the user cannot recognize the information displayed on the screen.
Further, the peripheral devices and circuits may successively be damaged due to a short-circuit resulting from the damage in the horizontal output circuit.
Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a display device with a power interruption delay function, in which a power interruption delay charging circuit is provided to prevent a horizontal output transistor from being damaged due to an instantaneous surge current generated when power supply is resumed under the condition that a high voltage charged on a horizontal deflection coil and an S-correction capacitor is not sufficiently discharged after power interruption.
In accordance with the present invention, the above and other objects can be accomplished by a provision of a display device with a power interruption delay function, comprising a pulse width modulation controller for generating a pulse width modulation signal under the control of a microcomputer; a current amplifier for amplifying current in response to the pulse width modulation signal from the pulse width modulation controller; an H/V processor for generating a square wave pulse signal under the control of the microcomputer; a horizontal driver for generating a drive pulse signal in response to the square wave pulse signal from the H/V processor; a horizontal deflection coil for horizontally deflecting electron beams; an S-correction capacitor connected in series to the horizontal deflection coil, for correcting a linearity of center-to-left and right sides of a screen; a horizontal output circuit for charging and discharging energy on the horizontal deflection coil and S-correction capacitor in response to an output signal from the current amplifier and the drive pulse signal from the horizontal driver; an H/V processor constant voltage circuit for supplying a constant voltage to the H/V processor; and power interruption delay charging means for gradually lowering an input voltage to the H/V processor constant voltage circuit when power supply to the display device is interrupted.